The goal of respiration systems is to relieve the respiratory muscles of the patient and to guarantee sufficient oxygen supply and carbon dioxide elimination. This happens either by the breathing work being assumed by a breathing drive either completely or partly in case of assisted methods. In view of the increase in chronic lung diseases and the need for improved therapy, noninvasive breathing support in case of improved interaction between patient and respiration drive is an important requirement for modern respiration systems. An essential aspect is the setting of the percentage that the device contributes to the breathing work relative to the percentage contributed to the breathing work by the patient himself/herself (corresponding to the amplitudes of the breaths) and the synchronicity in time. Various goals, e.g., relieving the patient's muscles or weaning from a respirator, can be pursued with an adjustable percentage of spontaneous breathing. It is important for this to detect the beginning of the phases of the patient's breathing with certainty, because this information does not unambiguously appear from the measured pneumatic signals of the respiration system, especially in neonates and COPD patients. It is known that electromyographic signals (EMG signals), which represent the activity of the breathing muscles, can be picked up to improve the adaptation to the patient's breathing efforts. Such a method is known from DE 10 2007 062 214 B3 (corresponding to U.S. Pat. No. 8,109,269). A breathing activity signal uEMG(t) is picked up with electrodes on the surface of the chest with the prior-art device. To make the electrode signals picked up into electromyographic signals representing the breathing activity, the electrode signals must be subjected to preprocessing; in particular, ECG signal components, which dominate the entire signal in terms of signal level, must be removed. Filtering as well as envelope detection may be performed for this. The envelope detection is preferably performed by absolute value determination or squaring and subsequent low pass filtering of the electrode signals. Electromyographic signals, which can be used to control the respiration drive of the respiration system, as is described, e.g., in DE 10 2007 062 214 B3, are obtained after this preprocessing.
It is also desirable during the respiration of patients to display an electrocardiogram (ECG) in order to have an overview of the vital parameters. This display shall be used to make visible the heart rate as well as the uniformity (variability) and irregularities (arrhythmia) in the display.
A plurality of electrodes are necessary for recording the electromyographic signals on the surface of the chest. If there are no cardiological issues, an ECG is usually recorded with three leads, i.e., four electrodes in the patient's chest region. If an ECG signal shall also be recorded besides an electromyographic signal, many electrodes must therefore be attached to the patient's upper body, which is disadvantageous especially for very small patients and premature babies.
Provisions are made according to DE 10 2009 035 018 A1 (corresponding to US 2011028819 A1), for the control device to be set up to pick up ECG signals from the electrode signals recorded before the ECG signal components are suppressed and to make data representative of the ECG available for display.
The electromyographic surface electrode signals, just as the signals of an esophageal EMG, do indeed contain a large signal component due to the cardiac activity (ECG signals). This signal component, with a signal amplitude of one to several mV, is eliminated from the signal curve in order to make it possible to rate the substantially lower other muscle activities (for example, diaphragmatic, intercostal and accessory respiratory muscles) as breathing activity signals. The ECG component is processed for this by subtracting or cutting out the ECG signals; as a rule, the signal components that contain an R peak of the ECG signal and cut out in a fixed time window before and after the R peak. The cut-out signal components are replaced either by 0 or a constant corresponding to the signal level before the time window of the R peak of the ECG signal, i.e., the signal is extrapolated over the time window with the signal level before the time window of the R peak. The eliminated ECG component of the electrode signals is not in a direct relationship with the patient's breathing efforts and is unremarkable in case of controlling breathing on the basis of the EMG signals. The EMG signals obtained after suppression of the ECG signal components are signals whose amplitude is modulated with the muscle activity.
The ECG signals present before they are suppressed can be picked up as ECG signals and displayed on a display. Leads, which approximately correspond to the usual leads of an ECG according to Einthoven I or II, are formed when the electrodes are positioned for detecting the EMG component. It is necessary for a diagnostic ECG to know the positions and hence the angles of view to the heart as a voltage generator (Cabrera circle) in order for the graphic representation to correspond to the modes of representation common in medicine and for the amplitude and time ratios to be able to be measured corresponding to the medical standards.
The electrodes are arranged at a patient module, which is to be placed on the surface of the patient's chest.